1. Field of the Invention
The present invention relates to non-reciprocal circuit devices, and, more particularly, to non-reciprocal circuit devices, such as isolators or circulators, for use in the microwave band.
2. Description of the Related Art
In general, non-reciprocal circuit devices, such as isolators or circulators, have a characteristic of transmitting a signal only in a given direction but not in the opposite direction. By utilizing this characteristic, for example, isolators are used in transmitting circuits of mobile communication devices, such as automobile phones and cellular phones.
As a non-reciprocal circuit device of the type described above, a two-port isolator is known, in which, as described in International Publication No. 2007/046229, first and second center electrodes are provided on first and second principal surfaces, which face each other, of a ferrite, and the first and second center electrodes are electrically connected at the first and second principal surface sides, respectively, through a conductive material that has been embedded in a recess provided in the end surface of the ferrite. Moreover, a three-port isolator is known in which, as described in Japanese Unexamined Patent Application Publication No. 2002-076711, the conductive material that has been embedded in the recess provided in the end surface of the ferrite is electrically connected to the center electrodes.
In isolators, a DC magnetic field is applied to a ferrite from permanent magnets. Isolators have problems in that, when a recess is provided in a ferrite, and then a conductive material is embedded therein, a magnetic field distribution in the ferrite is disturbed depending on the shape of the recess. As a result, insertion loss characteristics and isolation characteristics are deteriorated.